• 제목/요약/키워드: material transport

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HTL:EML(DPVBi:NPB)층의 조성비 변화에 따른 청색 유기 발광 소자 개발 (Development of Blue Organic Light-emitting Diodes(OLEDs) Due to Change in Mixed Ratio of HTL:EML(DPVBi:NPB) Layers)

  • 이태성;이병욱;홍진수;김창교
    • 한국전기전자재료학회논문지
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    • 제21권9호
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    • pp.853-858
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    • 2008
  • The structure of organic light-emitting diodes(OLEDs) with typical heterostructure consists of anode, hole injection layer, hole transport layer, light-emitting layer, electron transport layer, electron injection layer, and cathode. 4,4bis[N-(1-napthyl)-N-phenyl-amino]-biphenyl(NPB) used as a hole transport layer and 4'4-bis(2,2'-diphenyl vinyl)-1,1'-biphenyl(DPVBi) used as a blue light emitting layer were graded-mixed at selected ratio. Interface at heterojunction between the hole transport layer and the elecrtron transport layer restricts carrier's transfer. Mixing of the hole transport layer and the emitting layer reduces abrupt interface between the hole transport layer and the electron transport layer. The operating voltage of OLED devices with graded mixed-layer structure is 2.8 V at 1 $cd/m^2$ which is significantly lower than that of OLED device with typical heterostructure. The luminance of OLED devices with graded mixed-layer structure is 21,000 $cd/m^2$ , which is much higher than that of OLED device with typical heterostructure. This indicates that the graded mixed-layer enhances the movement of carriers by reducing the discontinuity of highest occupied molecular orbital(HOMO) of the interface between hole transport layer and emitting layer.

기상이동법에 의해 제조된 ZnO 결정의 형상 및 발광 특성에 미치는 TiO 첨가의 영향 (Effect of TiO Addition on Morphologies and Luminescence Properties of ZnO Crystals Fabricated by Vapor Transport Method)

  • 이근형
    • 한국재료학회지
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    • 제28권10호
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    • pp.590-594
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    • 2018
  • ZnO micro/nanocrystals are formed by a vapor transport method. Mixtures of ZnO and TiO powders are used as the source materials. The TiO powder acts as a reducing agent to reduce the ZnO to Zn and plays an important role in the formation of ZnO micro/nanocrystals. The vapor transport process is carried out in air at atmospheric pressure. When the weight ratios of TiO to ZnO in the source material are lower than 1:2, no ZnO micro/nanocrystals are formed. However, when the ratios of TiO to ZnO in the source material are greater than 1:1, the ZnO crystals with one-dimensional wire morphology are formed. In the room temperature cathodoluminescence spectra of all the products, a strong ultraviolet emission centered at 380 nm is observed. As the ratio of TiO to ZnO in the source material increases from 1:2 to 1:1, the intensity ratio of ultraviolet to visible emission increases, suggesting that the crystallinity of the ZnO crystals is improved. Only the ultraviolet emission is observed for the ZnO crystals prepared using the source material with a TiO/ZnO ratio of 2:1.

Controlled Charge Carrier Transport and Recombination for Efficient Electrophosphorescent OLED

  • Chin, Byung-Doo;Choi, Yu-Ri;Eo, Yong-Seok;Yu, Jai-Woong;Baek, Heume-Il;Lee, Chang-Hee
    • 한국정보디스플레이학회:학술대회논문집
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    • 한국정보디스플레이학회 2008년도 International Meeting on Information Display
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    • pp.1418-1420
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    • 2008
  • In this paper, the light emitting efficiency, spectrum, and the lifetime of the phosphorescent devices, whose emission characteristics are strongly dominated not only by the energy transfer but also by the charge carrier trapping induced by the emissive dopant, are explained by differences in the energy levels of the host, dopant, and nearby transport layers. On the basis of our finding on device performance and photocurrent measurement data by time-of-flight (TOF), we investigated the effect of the difference of carrier trapping dopant and properties of the host materials on the efficiency roll-off of phosphorescent organic light emitting diode (OLED), along with a physical interpretation and practical design scheme, such as a multiple host system, for improving the efficiency and lifetime of devices.

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Effect of Overlayer Thickness of Hole Transport Material on Photovoltaic Performance in Solid-Sate Dye-Sensitized Solar Cell

  • Kim, Hui-Seon;Lee, Chang-Ryul;Jang, In-Hyuk;Kang, Wee-Kyung;Park, Nam-Gyu
    • Bulletin of the Korean Chemical Society
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    • 제33권2호
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    • pp.670-674
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    • 2012
  • The photovoltaic performance of solid-state dye-sensitized solar cells employing hole transport material (HTM), 2,2',7,7'-tetrakis-(N,N-di-p-methoxyphenyl-amine)-9,9'-spirobifluorene (spiro-MeOTAD), has been investigated in terms of HTM overlayer thickness. Two important parameters, soak time and spin-coating rate, are varied to control the HTM thickness. Decrease in the period of loading the spiro-MeOTAD solution on $TiO_2$ layer (soak time) leads to decrease in the HTM overlayer thickness, whereas decrease in spin-coating rate increases the HTM overlayer thickness. Photocurrent density and fill factor increase with decreasing the overlayer thickness, whereas open-circuit voltage remains almost unchanged. The improved photocurrent density is mainly ascribed to the enhanced charge transport rate, associated with the improved charge collection efficiency. Among the studied HTM overlayer thicknesses, ca. 230 nm-thick HTM overlayer demonstrates best efficiency of 4.5% at AM 1.5G one sun light intensity.

정공수송층에 따른 백색 OLED의 발광 특성 (Emission Characteristics of White OLEDs with Various Hole Transport Layers)

  • 임병관;서정현;주성후;백경갑
    • 한국전기전자재료학회논문지
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    • 제23권12호
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    • pp.983-987
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    • 2010
  • In order to investigate the emission characteristics of the phosphorescent white organic light-emitting diodes (PHWOLEDs) according to various hole transport layers (HTLs), PHWOLEDs composed of HTLs whose structure are NPB/TCTA, NPB/mCP and NPB/TCTA/mCP, two emissive layers (EMLs) which emit two-wavelengths of light (blue and red), and electron transport layer were fabricated. The applied voltage, power efficiency, and external quantum efficiency at a current density of $1 mA/cm^2$ for the fabricated PHWOLEDs were 7.5 V, 11.5 lm/W, and 15%, in case of NPB/mCP, 5 V, 14.8 lm/W, and 13.7%, in case of NPB/TCTA, and 5.5 V, 14.6 lm/W, and 15%, in case of NPB/TCTA/mCP in the hole transport layer, respectively. High emission efficiency can be obtained when the amount of hole injection from anode is balanced out by the amount of electron injection from the cathode to EML by using NPB/TCTA/mCP structured HTL.

Numerical investigation on tortuosity of transport paths in cement-based materials

  • Zuo, Xiao-Bao;Sun, Wei;Liu, Zhi-Yong;Tang, Yu-Juan
    • Computers and Concrete
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    • 제13권3호
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    • pp.309-323
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    • 2014
  • Based on the compositions and structures of cement-based materials, the geometrical models of the tortuosity of transport paths in hardened cement pastes, mortar and concrete, which are associated with the capillary porosity, cement hydration degree, mixture particle shape, aggregate volume fraction and water-cement ratio, are established by using a geometric approach. Numerical simulations are carried out to investigate the effects of material parameters such as water-cement ratio, volume fraction of the mixtures, shape and size of aggregates and cement hydration degree, on the tortuosity of transport paths in hardened cement pastes, mortar and concrete. Results indicate that the transport tortuosity in cement-based materials decreases with the increasing of water-cement ratio, and increases with the cement hydration degree, the volume fraction of cement and aggregate, the shape factor and diameter of aggregates, and the material parameters related to cement pastes, such as the water-cement ratio, cement hydration degree and cement volume fraction, are the primary factors that influence the transport tortuosity of cement-based materials.

조석효과에 의한 항구 모델 주위의 유동 및 물질전달에 관한 실험적 연구 (Experimental study on the fluid flow and material transport around a harbor driven by the tidal effect)

  • 서용권;문종춘;강종대
    • 한국해양공학회지
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    • 제10권1호
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    • pp.100-107
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    • 1996
  • In this paper, we report the results of the experimental study on the flow and the mass transport around a square harbor driven by a tidal effect. The model harbor is composed of a uniform water-depth with a straight breakwater. The harbor is connected to the outer ocean by an entrance region having the same shape as the harbor. We investigated two cases, one having another breakwater in the place between the entrance region and the outer ocean, and the other without it, The surface and bottom flow patterns of the model container are visualized by using light particles and dye, respectively. It was shown that the inner harbor and the entrance region have well-organized, large vortical residual flows, and the material transport between the entrance and outer region is however significantly different for two cases; when the breakwater is built between the two regions, the transport is far better than that without it, which is clearly contrary to our common sense that the breakwater would block the dispersion of the materials between the harbor and the outer ocean.

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BCP 전자수송층 두께가 백색 OLED의 효율 및 발광 특성에 미치는 영향 (Effects of BCP Electron Transport Layer Thickness on the Efficiency and Emission Characteristics of White Organic Light-Emitting Diodes)

  • 서유석;문대규
    • 한국전기전자재료학회논문지
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    • 제27권1호
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    • pp.45-49
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    • 2014
  • We have fabricated white organic light-emitting diodes (OLEDs) using several thicknesses of electron-transport layer. The multi-emission layer structure doped with red and blue phosphorescent guest emitters was used for achieving white emission. 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) was used as an electron-transport layer. The thickness of BCP layer was varied to be 20, 55, and 120 nm. The current efficiency, emission and recombination characteristics of multi-layer white OLEDs were investigated. The BCP layer thickness variation results in the shift of emission spectrum due to the recombination zone shift. As the BCP layer thickness increases, the recombination zone shifts toward the electron-transport layer/emission-layer interface. The white OLED with a 55 nm thick BCP layer exhibited a maximum current efficiency of 40.9 cd/A.

사고전류 제한형 고온 초전도케이블의 통전부 특성평가 (Evaluation on the Properties of the Current Transporting Part for Fault-Current-Limiting Type HTS Cables)

  • 김태민;홍공현;한병성;두호익
    • 한국전기전자재료학회논문지
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    • 제27권10호
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    • pp.657-661
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    • 2014
  • When an abnormal condition occurs due to a fault current at a consumer location where electricity is supplied through high-Tc superconducting(HTS) cable, the HTS cable would be damaged if there is no appropriate method to protect it. The fault-current-limiting type HTS cable that is suggested in this study has a structure of transport part and limit part. It conduct a zero impedance transport current at ordinary operations and carry out a fault current limiting at extraordinary operations. To make a perfect this structure, it is essential to investigate electrical properties of transport part that comprise the fault-current-limiting type HTS cable. In this paper, transport part that comprise HTS wire with copper stabilization layer is examined the current transport properties and the stability evaluation.

Analysis of transport properties of SLS polysilicon TFTs

  • Fortunato, G.;Bonfiglietti, A.;Valletta, A.;Mariucci, L.;Rapisarda, M.;Brotherton, S.D.
    • 한국정보디스플레이학회:학술대회논문집
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    • 한국정보디스플레이학회 2006년도 6th International Meeting on Information Display
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    • pp.513-518
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    • 2006
  • An investigation of the transport properties of polysilicon TFTs, using sequential laterally solidified, SLS, material, is presented. This material has a location controlled distribution of grain boundaries, GBs, which makes it particularly useful for the analysis of their influence on the performance of polysilicon TFTs, and to address the issue of the role of spatially localised trapping states. The experimental results were analyzed by using numerical simulations, and the effective medium approximation was compared with a discrete grain model.

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